Issue 36

R. Citarella, Frattura ed Integrità Strutturale, 36 (2016) 160-167; DOI: 10.3221/IGF-ESIS.36.16

Multiple crack propagation by DBEM in a riveted butt-joint: a simplified bidimensional approach

R. Citarella (https://orcid.org/0000-0003-3167-019X) Dept. of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132, Fisciano (SA), Italy rcitarella@unisa.it

A BSTRACT . A Multi-Site Damage (MSD) crack growth simulation is presented, carried out by means of Dual Boundary Element Method (DBEM), in a two-dimensional analysis of a cracked butt-joint made of aluminium 2024 T3. An equivalent crack length is proposed for an approximated 2D analysis of a 3D problem where the crack front assumes a part elliptical shape due to secondary bending effects. The assumptions made to perform such simplified bidimensional analyses are validated by comparing numerical results with experimental data, the latter obtained from a fatigue tested riveted butt-joint. K EY WORDS : DBEM; MSD; LEFM.

I NTRODUCTION

C

omplex engineering structures will often present microscopic flaws that can be caused by the manufacturing process or by fatigue, impact or environmental effects such as corrosion. It is therefore crucial to be able to predict how these cracks will affect the integrity of the structure, for example to determine whether a particular crack will grow at all under service loading and, in case, what the life of the component before failure. It is evident from this considerations that the field of Fracture Mechanics will be an integral part of the design process, particularly in the aircraft industry due to the high strength but low crack resistance materials used in weight critical applications. Experimental studies have shown that, if the hypothesis of Linear Elastic Fracture Mechanics (LEFM) holds true, failure occurs when the Stress Intensity Factor (SIF) reaches a critical value. Hence the predictions of crack behaviour and the integrity of a structure are dependent on the accurate calculation of SIFs.

(a)

(b) Figure 1 : Deformed lap-joint undergoing a traction load with highlight of sites undergoing maximum bending stresses (a) and stress distribution through the thickness of the sheet (b).

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